The practice of tagging petroleum fuels with chemicals for purposes such as tax identification, brand identification, etc. is well established. Such markers are described, for example, in U.S. Pat. Nos. 4,209,302, 4,735,631, 5,205,840, and 5,252,106. These markers are added to petroleum fuels at low levels, e.g., in the 1-100 parts per million by weight (ppm) range. Subsequently, the markers are extracted from the fuel with an acidic or basic aqueous solution and either undergo a chromophoric change caused by the extractant or are simultaneously or subsequently reacted with a reagent which causes it to undergo a chromophoric reaction. While markers such as these have been the standard of the industry, the wet chemistry involved poses certain disadvantages. In particular, the fuel sampled for identification, when exposed to the extractant, cannot be returned to its source. Though the amount of fuel taken for sampling is generally small, the sampled fuel, along with the extracting reagent, require disposal. Increasingly stringent environmental requirements prevent on-site disposal of even small amounts of fuel and fuel-containing specimens. Rather, such samples must be disposed of as hazardous wastes.
Because of the disadvantages of wet chemistry, there is a movement toward tagging and identification methods which are non-destructive in the sense that the fuel specimen may be returned to the reservoir from which it was taken. Recently, Morton International, Inc. has introduced a portable infrared spectrometer with data processing capabilities, sold under the trademark SpecTrace such that one, and preferably more than one, marker can be identified and quantified directly in a specimen of the fuel. As the fuel is exposed to no contaminating chemicals, the specimen can be returned to its source. This apparatus provides for simple and accurate quantitative testing of gasolines in the field.
Truly silent markers which are not visible at any concentration have also been proposed for invisibly tagging petroleum products. These markers are typically large organic molecules that have virtually no absorbance in the visible portion of the spectrum and that absorb and/or fluoresce in the near infrared to mark their presence in a fuel sample. U.S. Pat. No. 5,525,516 (Krutak et al.) and European Patent 0,656,929 (Albert et al.) describe such markers. In these references, the presence of such a marker is detected in the fuel by exposing the fuel to near infrared radiation and then either detecting the characteristic light absorption spectra of the marker or its emitted fluorescent light in the near infrared region with standard absorption or fluorescent detection equipment. While the detection procedure is much simpler, molecules or markers that are active in near infrared are large, complex, organic structures. Therefore, these markers are difficult and expensive to make. Furthermore, there are only a finite number of near infrared absorbing or fluorescing molecules that can serve as silent markers.
There is a continuing need for markers which can be identified spectrophotometrically for identification in SpecTrace or other instruments. There are a number of criteria for such markers. A marker should have at least one strong absorbency peak in a spectral region in which the fuel, fuel additives, and natural contaminants to the fuel do not absorb. Preferably, the marker is colorless so as to serve as a "silent" marker, although a lightly colored marker may be masked by dyes added to the gasoline. The marker must be non-reactive with the fuel and other fuel additives and must be in no way harmful to the engine in which the fuel is used. Although the marker is added to the fuel at a low level in the fuel, e.g., between about 0.25 and about 100 ppm, it is preferably highly soluble within the fuel. More importantly, a fuel marker should be insoluble in aqueous solutions or substantially so, preferably having a solubility in water of less than about 0.2 g per 100 ml. of water at 20.degree. C. The marker should not be easily removable from the fuel.
A variety of different markers are required for the petroleum fuel industry. With a wide number of taxing bodies throughout the world, a large number of petroleum producers and a variety of different petroleum fuel products, there is a need for individualizing marker systems for different products and different tax levels.
While petroleum fuels are perhaps the most commonly tagged materials, other materials are increasingly being tagged for identification and protection against adulteration. The variety of materials so tagged is expected to increase. Examples of materials that are or may potentially be tagged include refrigerant lubricants, pharmaceuticals, cosmetics, food, liquor, soft drinks, paints, polymers, agricultural chemicals, and rubber. Each of such materials will have individual requirements.